Development of a cross-linked epoxy resin with flame-retardant properties

ABSTRACT

The invention discloses a cross-linked epoxy resin with flame-retardant properties and method for producing the same. The polymeric material of the invention includes an epoxy resin, a curing agent and a modification agent. Particularly, the modification agent is a derivative of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). Moreover, the curing agent is 4,4′-diaminodiphenyl methane (DDM), or tris(4-aminophenyl)amine (NNH).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention application is a divisional application of U.S.patent application Ser. No. 12/276,654, which claims the benefit of theearlier filing date of Nov. 24, 2008, and relates to a cross-linkedepoxy resin and method for producing the same; particularly, the epoxyresin of the invention with flame-retardant properties has betterthermal stability and mechanical property.

2. Description of the Prior Art

Epoxy resin is widely used in many domains such as paint, adhesive,building materials, electric packing materials, etc. Because it has manyadvantages such as no small molecules forming during curing process, lowshrinkage rate for finished products, low strain, resistant to acid,alkali and other chemical solutions, good adherence, good insulation,light weight, low cost, easy to treat, etc. In recent years, epoxy resineven gradually replaces traditional materials to be used in hightechnology regions such as electric information, mechanical engineering,aerospace engineering, etc.

However, poor mechanical property and inflammability of epoxy resinoften induce unexpected defect on products of top technology regionssuch as electronics, composite materials, etc. Therefore, how to improvethe mechanical property and inflammability of epoxy resin becomes apopular research direction.

There are mainly three common methods for modifying the epoxy resin:

(1) Introducing non-reaction type of long chain molecules, for example,natural or synthetic rubber, and so on.

(2) Introducing reaction type of long chain molecules. For example,imide oligomer, aromatic polyester, etc.

(3) Increasing the cross-linked density or the intramolecularinteractions.

It is effective to enhance the flexibility of epoxy resin by addingrubber or thermoplastic particle. However, this method also decreasesits glass transition temperature, yield stress and heat stability at thesame time. In recent years, many researches have shown that they caneffectively raises the flame-retardant and heat-resistant properties ofpolymeric materials by introducing a phosphorus-containingflame-retardant agent and replacing the halogens by other elements.Since the phosphorus-containing flame-retardant agent has manyadvantages such as hypotoxicity, low smoking generation and lowrecruitment, there is a tendency toward developing thephosphorus-containing flame-retardant agent in recent years.

In general, there are two ways to get a flame-retardant epoxy resin:

One is adding a flame-retardant agent to an epoxy resin. The other isdirectly introduction of flame-retardant elements into the molecularstructures of an epoxy resin or a curing agent.

However, there are some disadvantages to raise the effect offlame-retardant by adding a flame-retardant agent. First, it will inducepoor compatibility between the flame-retardant agent and the epoxyresin. Second, it will influence the workability of the epoxy resin.Third, the flame-retardant agent easily migrates to the surface of anobject. However, the reaction type flame-retardant agent has advantagesof preventing migration, less contamination, better durability, waterresistance, etc., so that the reaction type flame-retardant agent hasbecome a research focal point in recent years.

In 1996, M. D. Shau et al. synthesized a phosphoric tri-amine compound(TAPO) to be the epoxy resin curing agent to carry on the research ofthe flame-retardant nature. In 1999, M. D. Shau used the phosphoricamines curing agent (BAMPO) to prepare the phosphoric epoxy resin, andthen it achieved the effect of flame-retardant. In 1999, C. S. Wang etal. took DOPO phosphoric group as main bodies, developed a series of aphosphoric group curing agent, a phosphoric epoxy resin and a phosphoricepoxy resin half solidification which have high glass transitiontemperature, high heat-resistant property and extremely goodflame-retardant property. It is important to note that9,10-Dihydro-9-oxa-10-phosphaphenthrene (DOPO) is a kind of phosphoricorganic compound, developed in 1970, and its reactive hydrogen is easyto react with electrophilic compounds such as rosolic acid,benzoquinone, bismaleimide, oxirane, diaminobenzophenone, maleic acid,cyanate ester terephthaldicarboxaldehyde, and so on. DOPO can be used tobe the forerunner of a flame-retardant additive or a reaction typeflame-retardant agent.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the present invention is to provide a novelcross-linked flame-retardant epoxy resin of polymeric material and themanufacturing method of the same. By using the way of chemical bondingor introduction of the phosphoric structure to be combined withpolymeric structure, the new heat-resistant cross-linked epoxy resin ofpolymeric material is developed.

According to an embodiment of the invention, the polymeric materialincludes an epoxy resin, a curing agent and a modification agent.Particularly, the curing agent is 4,4′-diaminodiphenyl methane (DDM) ortris(4-aminophenyl)amine (NNH). Furthermore, the modification agent is aderivative of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)(Dopo-tri-azetidine-2,4-diones is preferred.)

According to another embodiment of the invention, the method formanufacturing a novel cross-linked epoxy resin comprising the followingsteps:

(a) Preparing a modification agent.

(b) Adding a curing agent and the modification agent into an epoxyresin.

(c) Utilizing the result of step (b) under a curing temperature with acuring time to obtain the novel cross-linked epoxy resin.

As mentioned above, the modification agent is a derivative of DOPO, andDopo-tri-azetidine-2,4-diones is preferred. Moreover, the curing agentis DDM or NNH.

The objective of the present invention will no doubt become obvious tothose of ordinary skill in the art after reading the following detaileddescription of the preferred embodiment, which is illustrated in thevarious figures and drawings.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 is a reaction diagram according to an embodiment of theinvention.

FIG. 2 is a synthesis reaction diagram of MIA according to theinvention.

FIG. 3 is a synthesis reaction diagram of Dopo-tri-azetidine-2,4-dionesof the invention.

FIG. 4(A) and FIG. 4(B) are the FTIR spectrograms before and after thesynthesis reaction of Dopo-ta with MIA.

FIG. 5(A) is a storage modulus comparison diagram for polymericmaterials made by different ratios of raw materials. (DDM is the curingagent)

FIG. 5(B) is a damping parameter comparison diagram for polymericmaterials made by different ratios of raw materials. (DDM is the curingagent)

FIG. 6(A) is a storage modulus comparison diagram for polymericmaterials made by different ratios of raw materials. (NNH is the curingagent)

FIG. 6(B) is a damping parameter comparison diagram for polymericmaterials made by different ratios of raw materials. (NNH is the curingagent)

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for producing a novelcross-linked epoxy resin with flame-retardant properties by chemicalbonding or introduction of phosphoric structure in polymeric structure.Particularly, in an epoxy modification reaction of the presentinvention, the phosphoric reaction type modification agentDopo-tri-azetidine-2,4-diones is selected to combine with the primaryamine to carry on the ring opening reaction by using thermo-chemicalreaction under room temperature, to form the malonamide functionalgroup, to produce the physical cross-linking sites via hydrogen bondingand to improve the mechanical property effectively. In addition, theintroduction of the phosphoric DOPO structure could be able to enhancethe flame-retardant property of the epoxy resin effectively.

In short, this invention is by using Dopo-tri-azetidine-2,4-diones andepoxy resin reacting with diamine and triamine respectively to producethe net cross-linked structure; additionally, by using the malonamidefunctional group to generate the physical cross-linking hydrogen bonds,to achieve the improve mechanical property of the epoxy resin and itsthermal stability. Please refer to FIG. 1, which shows a reactiondiagram according to an embodiment of the invention. As shown in FIG. 1,the method of the invention can produce a net type cross-linked highpolymeric material.

The following describes several embodiments of the present inventionabout the manufacturing method of the novel cross-linked flame-retardantepoxy resin.

Embodiment 1 Composing4-isocyanate-4-(3,3-dimethyl-2,4-dioxo-azetidino)diphenyl methane (MIA)

Please refer to FIG. 2, which is a synthesis reaction diagram of MIAaccording to the invention. First, methylenedi-p-phenyl diisocyanate(MDI) and isobutyryl chloride (IBUC) with equal equivalent are dissolvedin xylene, and then the solution is continuously heated and stirred forseveral hours. Then, equal equivalent triethylamine (TEA) is added tosaid solution and the temperature is lowered to 0° C. Consequently, anorange solid material is formed. Next, the solution is filtered and thefiltrate is recrystalized and purified with cyclohexane, so as to obtainMIA. The yield rate of MIA is approximately 45%. In addition, we may useNMR, EA and Mass to confirm the structure of the synthesized MIA.

In this embodiment, MDI, IBUC and TEA all can be purchased from ACROS.Wherein, MDI is a faint yellow solid and can be used directly withoutpurification. The molecular formula of MDI is C₁₅H₁₀N₂O₂, the molecularweight is 250.26, and the melting point is 37-39° C. IBUC is atransparent liquid and can be used directly without purification. Themolecular formula of IBUC is C₄H₇Cl₂O; the molecular weight is 106.55,and the boiling point is 91-93° C. TEA is also a transparent liquid andcan be used directly without purification. The molecular formula of TEAis C₆H₁₅N; the molecular weight is 101.19, and the boiling point is88.9° C. Certainly, in practice, the raw materials mentioned above maybe purchased from other suppliers and the raw materials with differentphysicochemical characteristics may be chosen based upon differentsituations.

Embodiment 2 Composing the Modification AgentDopo-tri-azetidine-2,4-diones

Please refer to FIG. 3, which is a synthesis reaction diagram ofDopo-tri-azetidine-2,4-diones according to the invention. Firstly, have9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide (DOPO) purchased fromTCI and MIA of embodiment 1 dissolve in DMF in a proportion of moleratio 1:3. Then, stir the mixture for several hours at 80° C. Afterward,drip the mixture into a solution of methanol to carry on reprecipitaionreaction, wherein the ratio of methanol and water of the solution is1:1. Finally, carry on the Soxhlet extraction method to the obtainedprecipitate, wash off the unneeded small molecules by methanol, andobtain a white product. The yield rate of the white product isapproximately 95%. DOPO-ta used in the embodiment is a purple solid andsynthesized from the nucleophilic addition reaction of DOPO andpararosaniline chloride. The molecular formula of DOPO-ta isC₃₁H₂₆N₃O₂P; the molecular weight is 504, and the melting point is 329°C. Certainly, in practice, the DOPO may also be purchased from othersuppliers and the raw materials with different physicochemicalcharacteristics may be chosen based upon different situations.

In the embodiment, a Fourier Transform Infrared Spectroscopy (FTIR) maybe used to monitor the reaction of the Dopo-ta with MIA. Please refer toFIG. 4(A) and FIG. 4(B), which are the FTIR spectrograms before andafter the synthesis reaction of Dopo-tri-azetidine-2,4-diones. As shownin FIG. 4(A), 1740 cm⁻¹ and 1878 cm⁻¹ are the special absorption peaksof azetidine-2,4-dione functional group, while 2262 cm⁻¹ is the specialabsorption peak of isocyanate functional group. In addition, as shown inFIG. 4(B), 1740 cm⁻¹ and 1856 cm⁻¹ are the special absorption peaks ofthe azetidine-2,4-dione functional group, while the special absorptionpeak of isocyanate functional group (2262 cm⁻¹) is disappeared becauseof reactions. Moreover, 1190 cm⁻¹ is the special absorption peak ofphosphine oxide functional group, and 3348 cm⁻¹ is the specialabsorption peak of the secondary amide functional group.

Embodiment 3 Composing the Novel Cross-Linked Flame-Retardant EpoxyResin of this Invention

In the embodiment, the epoxy resin of FIG. 1 is mixed withDopo-tri-azetidine-2,4-diones composed from embodiment 2 and a curingagent to synthesize the novel cross-linked flame-retardant epoxy resinof this invention. In the embodiment, the product BE 187 of Nan YaPlastic Corp. is selected as the epoxy resin. BE 187 is a transparentsticky liquid and can be used directly without purification. The epoxideequivalent of BE 187 is 187 g/equiv. The curing agent separately uses4,4′-diaminodiphenyl methane (DDM) or tris(4-aminophenyl)amine (NNH).Among which, DDM, bought from ACROS, is a yellow solid and can be useddirectly without purification. The molecular formula of DDM is C₁₃H₁₄N₂,the molecular weight is 198.27, the boiling point is 398° C. and thestructural formula is as follows:

In addition, the embodiment selects the structural formula of the NNH isas follows:

Certainly, in the practice, the epoxy resin and the curing agent may bepurchased from other suppliers and the raw materials with differentphysicochemical characteristics may be chosen based upon differentsituations.

In the embodiment, the aforementioned epoxy resin, the curing agent andthe modification agent are mixed with each other separately and cured at140° C., 180° C., and 220° C. each for 2 hours to prepare the highpolymeric material of the invention. And, the curing temperatures, thecuring time as well as the various proportions of raw materials willaffect the thermal property and the mechanical property of the highpolymeric material. The following will analyze the thermal property andthe mechanical property of the high polymeric material in the inventionby several embodiments.

Embodiment 4 The Analysis of the Thermal Property of the NovelCross-Linked Epoxy Resin in the Invention

Please refer to the following table 1, which shows the DSC glasstransition temperatures of the cross-linked epoxy resin high polymericmaterials formed by different proportions of raw materials and differentcuring temperatures. In the embodiment, the curing time is 2 hours.

TABLE 1 The Equivalent Ratio (the epoxy resin:the curing agent: TheCuring Temperature NO the modification agent) 140° C. 180° C. 220° C. 11:1.1:0.1 148° C. 163° C. 167° C. 2 1:1.2:0.2 132° C. 156° C. 162° C. 31:1.3:0.3 126° C. 161° C. 164° C. 4 1:1.5:0.5 112° C. 160° C. ND 51:1.1:0.1 ND ND ND 6 1:1.2:0.2 167° C. 180° C. ND 7 1:1.3:0.3 ND ND 200°C. 8 1:1.5:0.5 ND ND ND The curing agent of No. 1 to No. 4 is DDM; whilethe curing agent of No. 5 to No. 8 is NNH. ND: Glass transitiontemperature is not detectable.

Please refer to the following table 2, which lists the DSC and TGA valueof different proportions of raw materials.

TABLE 2 The curing agent/ the epoxy resin/ NO the modification agent Tg^(a) Tg ^(b) Td ^(c) char yield ^(d) 1 1/1/0 166 153 363 15.1 21.1/1/0.1 168 159 317 18.7 3 1.3/1/0.3 164 142 334 23.3 4 1.5/1/0.5 ND127 320 25.3 5 1/1/0 ND 113 327 26.2 6 1.1/1/0.1 ND 150 318 32.1 71.3/1/0.3 200 151 301 31.7 8 1.5/1/0.5 ND 145 306 33 The curing agent ofNo. 1 to No. 4 is DDM; while the curing agent of No. 5 to No. 8 is NNH.^(a) in a nitrogen environment, Tg obtained from DSC at a heating rateof 10° C./min ^(b) in a nitrogen environment, Tg obtained from DMA at aheating rate of 5° C./min ^(c) in a nitrogen environment, 5% weight lossT_(d) obtained from TGA at a heating rate of 10° C./min ^(d) in anitrogen environment, char yield obtained from TGA at a heating rate of10° C./min to the temperature 750° C. ND: can't detect the glasstransition temperature

Embodiment 5 The Analysis of the Mechanical Property of the NovelCross-Linked Epoxy Resin in the Invention

Please refer to FIG. 5(A) and FIG. 5(B). FIG. 5(A) is the storagemodulus comparison diagram of high polymeric materials prepared bydifferent proportions of raw materials; while FIG. 5(B) shows thedamping parameter comparison diagram of high polymeric materialsprepared by different proportions of raw materials. Please note thatboth of the high polymeric materials showed in FIG. 5(A) and FIG. 5(B)use DDM as the curing agent and Dopo-tri-azetidine-2,4-diones as themodification agent.

Please refer to FIG. 6(A) and FIG. 6(B). FIG. 6(A) is the storagemodulus comparison diagram of high polymeric materials prepared bydifferent proportions of raw materials; while FIG. 6(B) shows thedamping parameter comparison diagram of high polymeric materialsprepared by different proportions of raw materials. Please note thatboth of the high polymeric materials showed in FIG. 6(A) and FIG. 6(B)use NNH as the curing agent and Dopo-tri-azetidine-2,4-diones as themodification agent.

Please refer to the following table 3; it is the DMA data summary tableof the embodiment.

TABLE 3 The Ratio of the curing storage modulus ^(a) agent/the epoxyresin/ At 100° C. Loss modulus ^(a) Tandpeak NO the modification agent(MPa) (MPa) (° C.) Tandmax 1 1/1/0 1.758 1.163 177.3 0.327 2 1.1/1/0.11.203 1.53 168.6 0.506 3 1.3/1/0.3 3.14 3.43 154.1 0.359 4 1.5/1/0.50.987 1.4 142.1 0.7 5 1/1/0 0.67 0.732 134.4 0.408 6 1.1/1/0.1 1.64 1.56186 0.33 7 1.3/1/0.3 1.81 1.6 175.2, 221 0.327, 0.256 8 1.5/1/0.5 2.131.67 164.7, 242 0.326, 0.234 The curing agent of No. 1 to No. 4 is DDM;while the curing agent of No. 5 to No. 8 is NNH. ^(a) in a nitrogenenvironment, the result obtained at a heating rate of 5° C./min

Please refer to the following table 4; it is a weight percentage datasummary table of each composition proportion for this embodiment.

TABLE 4 The Ratio of the curing agent/the epoxy resin/ DDM NNH BEDopo-tri-azetidine-2,4- NO the modification agent (wt %) (wt %) (wt %)diones (wt %) 1 1/1/0 21 0 79 0 2 1.1/1/0.1 24.13 0 75.8 19.8 31.3/1/0.3 19.2 0 45 35.0 4 1.5/1/0.5 18.7 0 35 46.0 5 1/1/0 0 20.6 79.40 6 1.1/1/0.1 0 19.8 63.64 16.6 7 1.3/1/0.3 0 18.8 45.5 35.7 8 1.5/1/0.50 18.3 35.4 46.3 The curing agent of No. 1 to No. 4 is DDM; while thecuring agent of No. 5 to No. 8 is NNH.

Result and Discussion

(1) Thermal Property Discussion

a. Take DDM as the curing agent

Along with the curing temperature rises, the cross-linked density andT_(g) also increase. After introducing the reaction type modificationagent of the phosphoric Dopo-tri-azetidine-2,4-diones, it is found thatwhen the introduction content of the phosphoricDopo-tri-azetidine-2,4-diones increases at the curing temperature 220°C., T_(g) drops. Along with the content increase of the phosphoricDopo-tri-azetidine-2,4-diones, T_(g) maintains above 127° C. and T_(d)is around 320° C. In the char yield study, it is obvious to note thatalong with the increase of the quantity of theDopo-tri-azetidine-2,4-diones, the char yield increases from 15.1 to25.3.

b. Take NNH as the curing agent

When the equivalent ratio of the functional group of the introducedmodification agent increases from 0 to 0.1, the temperature of T_(g)rises from 113° C. to 151° C. Along with the content of the curing agentincreases, the cross linking density also increases. Moreover, T_(g)sall maintain above 145° C. and T_(d)s all maintain above 300° C. Fromthe above data, it is known that the increase of introduction of theDopo-tri-azetidine-2,4-diones content not only increases the char yieldbut also becomes helpful for the promotion and maintenance of thethermal stability.

(2) Mechanical Property Discussion

a. Take DDM as the curing agent

In the equivalent ratios of the Dopo-tri-azetidine-2,4-diones'functional group 0.1 and 0.3, the storage modulus and the loss modulushave a more obvious promotion (the storage modulus promotes from 1.2 to3.14, while the loss modulus promotes from 1.53 to 3.43). When theequivalent ratio of the modification agent increases to 0.5, theincrease of the phosphoric quantity will let the thermal stabilityslightly drop to 127° C. It's because the weight percentage ofDopo-tri-azetidine-2,4-diones is 46%, but the epoxy resin just only 35%.But the material still possess high loss modulus.

b. Take NNH as the curing agent

Along with the increase of the modification agent content, the storagemodulus and the loss modulus have obvious promotion (the storage modulusrises from 1.64 to 2.13, while the loss modulus rises from 1.56 to1.67). In addition, in different proportions, to compare the NNH withthree functional groups to the DDM with double functional groups, theT_(g) of the NNH obtains a higher tand than that of the DDM. It isbecause the three-functional-groups NNH has more reaction points thanthe double-functional-groups DDM to form a cross-linked epoxy resinstructure with a higher cross-linked density. Therefore, the improvementrange of the mechanical property becomes more obvious. Especially, thereare two peaks in the tand chart, and along with the more the increase ofthe Dopo-tri-azetidine-2,4-diones, the more the right side peak shiftstoward the right lateral and the bigger its obvious degree is. Theestimation is the promotion of the modification agent proportion enablesthe hard chain of the DOPO structure to form a copolymer form. However,it keeps a good toughness in the meanwhile of the raising T_(g). It isextrapolated that the azetidine-2,4-dione functional group heats upring-opening to form the malonamide functional group, so as tosynthesize the malonamide with multi-hydrogen bonds.

To sum up, in the formula of the Dopo-tri-azetidine-2,4-diones content0.1, the improvement effect is not so obvious due to the lessrecruitment. Along with the enhancement of the recruitment to theproportion 0.3 to form the cross-linked epoxy resin, it may make thematerial not only keep very high T_(g) (142° C.˜151° C.) but also enableT_(d) maintain between 301° C. and 334° C. In addition, by introducingthe Dopo-tri-azetidine-2,4-diones reaction type modification agent intothe epoxy resin, curing ring-opening is heated up to produce thehydrogen bond and to increase the physical and chemical bonding of theepoxy resin; as a result, it promotes the storage modulus and the lossmodulus of the material substantially. Also, it keeps the rigidity ofthe material and its toughness simultaneously. The method overcomes theproblems of high temperature hardening of the epoxy resin (e.g. hardnessand crispness); moreover, it improves the mechanical property and thethermal stability of the epoxy resin.

Although the present invention has been illustrated and described withreference to the preferred embodiment thereof, it should be understoodthat it is in no way limited to the details of such embodiment but iscapable of numerous modifications within the scope of the appendedclaims.

1. A method for manufacturing a cross-linked epoxy resin comprising thefollowing steps: (a) preparing a modification agent; (b) adding a curingagent and the modification agent into an epoxy resin; and (c) utilizingthe result of step (b) under a curing temperature with a curing time toobtain the novel cross-linked epoxy resin.
 2. The method of claim 1,wherein the epoxide equivalent of the epoxy resin is 187 g/equiv.
 3. Themethod of claim 1, wherein the curing agent is 4,4′-diaminodiphenylmethane (DDM) or tris(4-aminophenyl)amine (NNH).
 4. The method of claim1, wherein the modification agent is Dopo-tri-azetidine-2,4-diones. 5.The method of claim 1, wherein the equivalent ratio of the modificationagent, the epoxy resin and the curing agent is 0.1-0.5:1:1-1.5.
 6. Themethod of claim 1, wherein the curing temperature is between 140° C. and220° C.
 7. The method of claim 6, wherein the curing temperature is 140°C., 180° C., or 220° C.
 8. The manufacture method of claim 1, whereinthe curing time is 2 hours.